Introduction / Context:
A Schmitt trigger is a comparator with positive feedback that exhibits hysteresis. Its most important practical specifications are the two switching thresholds (upper and lower), the hysteresis width, and the relationship between input voltage and output state. A transfer function graph (sometimes called a voltage transfer characteristic) captures these facts in a single, intuitive plot.
Given Data / Assumptions:
- The device is a Schmitt trigger (inverting or non-inverting topology).
- Transfer function graph plots V_out versus V_in and indicates threshold points.
- Supply rails and logic output levels are within normal operating conditions.
Concept / Approach:
The Schmitt trigger’s hallmark is hysteresis: the rising-input threshold V_T+ and the falling-input threshold V_T− are different values, separated by a hysteresis width H = V_T+ − V_T−. A transfer graph shows the direction-dependent switching: as V_in rises past V_T+, the output snaps to the opposite rail; as V_in falls past V_T−, it snaps back. This visual directly communicates noise immunity and the input margin that prevents chatter near a single threshold.
Step-by-Step Solution:
Identify V_T+ on the rising trajectory where the output toggles.Identify V_T− on the falling trajectory where the output toggles back.Compute hysteresis width H = V_T+ − V_T−; this is the noise band immune to spurious switching.Relate output levels to supply rails (e.g., logic HIGH and LOW).
Verification / Alternative check:
Datasheets list V_T+, V_T− and often include a transfer plot; the plot matches tabulated thresholds and shows the “loop” that embodies hysteresis.
Why Other Options Are Wrong:
Incorrect: Ignores that thresholds and hysteresis are literally read off the transfer curve.Only true for non-inverting types: Inverting and non-inverting both have transfer curves that show thresholds.True only at 25 °C: While values vary with temperature, the graph form and what it illustrates remain valid.
Common Pitfalls:
Confusing a simple comparator (single threshold) with a Schmitt trigger (two thresholds).Reading a DC transfer plot as if it were a dynamic timing diagram; it is quasi-static behavior.
Final Answer:
Correct
Discussion & Comments